Experimental and Numerical Study via CFD of A Rotating Drum Dimensioning Applied in the Microwave‐Assisted Convective Drying of Specialty Coffees

Rotary drums are renowned for their flexibility, simple operation, and high production rates. Microwave dryers offer energy savings, reduced drying times, lower operating costs, and improved product quality. An experimental–numerical study was conducted to design and validate a microwave‐assisted convective rotary drum dryer for specialty coffees. Computational fluid dynamics (CFD) simulations determined the optimal drum volume (175.98 L; height 56.5 cm; diameter 62.98 cm), nine two‐segment hangers to maximize bean exposure to electromagnetic hotspots, a drum fill ratio of 30%, and a rotation speed of 2 rpm. The simulations showed good agreement with the experimental results. The prototype was tested with Coffea arabica cv. Arara beans using a three‐stage drying sequence: sun pre‐drying, convective drying at 40°C, and final microwave‐assisted rotary drying at a fixed power of 997.48 W. The product was subjected to a cupping test. The prototype reduced the drying time for washed coffee to 11.75 and for cherry coffee to 27.47 h, with energy consumption of 4.42 and 8.97 kWh, respectively, compared to 19.7 h and 23.38 kWh in the drying oven, while maintaining comparable sensory quality, with scores ranging from 74 to 80 points.